1. Field of the Invention
The present invention generally relates to a photo diode (PD) that converts incident light into an electrical signal. More particularly, the present invention generally relates to a photo diode having improved energy efficiency, and a method for manufacturing same.
A claim of priority is made to Korean Patent Application No. 2004-37330, filed on May 25, 2004, the disclosure of which is incorporated by reference herein.
2. Description of the Related Art
A photo diode is a common optical element used in a semiconductor device. The photo diode receives light and converts it into an electrical signal (current or voltage). Conventional methods for manufacturing the photo diode include: a method of utilizing a PN junction, a method for manufacturing a P-type electrode, including an intrinsic epitaxial layer—N+-type layer—P-type substrate (PIP) type, and an N-type electrode, including an intrinsic epitaxial layer—P+-type layer—P-type substrate (NIP) type, and a method of using an avalanche breakdown PD (APD).
However, a photo diode using a PN junction operates at low speed and has limited frequency characteristics. The APD generates large noise and requires high operating power. Thus, the NIP and PIN structure photo diodes have conventionally been preferred.
The NIP and PIN structure photo diodes are generally used in optical pickup devices such as CD-ROM, CD-R/RW, DVD-ROM, and DVD-R/RW. The photo diode is used to read data from a disc and/or write data to a disc. Additionally, the photo diode functions as an interface to transmit a signal to a servo.
FIG. 1 is a sectional view illustrating a conventional NIP structured photo diode. In FIG. 1, a P+-type buried layer 2, a P-type epitaxial layer 3, an N-type epitaxial layer 5, and an N+-type highly doped layer 8 are sequentially formed on a substrate 1. A P-type first junction region 4 and a P-type second junction region 6 are formed and connected with each other in P-type epitaxial layer 3 and N-type epitaxial layer 5, respectively. Further, a P+-type layer 9b is formed in P-type second junction region 6 and is in contact with an anode electrode metal contact plug 13a. A P+-type partition layer 9a is formed on N-type epitaxial layer 5 to partition a light receiving portion of the photo diode, which functions as a window to receive light. Metal wire structures 13a, 13b, 15a, and 15b, and the anode electrode are insulated from their peripheries by an interlayer dielectric film 12 and an inter-metal dielectric film 14. Additionally, a device isolation layer 7, such as LOCOS, is used to isolate the photo diode from other peripheral devices are formed on substrate 1. Further, a silicon oxide film 20a and a silicon nitride film 20b are formed as an anti-reflective coating (ARC) layer 20 to suppress the reflection of incident light on the entire surface including the light receiving portion of the photo diode.
The photo diode is evaluated by light efficiency and frequency characteristics (or bandwidth). An excellent performing photo diode should have high photoelectric-conversion efficiency at a detected light wavelength, and should also have high response speed. Various studies and developments are under progress to improve the performance of the photo diode.
In particular, the reflection of incident light from the light receiving portion of the photo diode must be suppressed to increase the light efficiency at the detected wavelength. ARC layer 20 of FIG. 1 is formed on an upper surface of the light receiving portion to reduce this reflection. The type and thickness of ARC layer 20 is selected based on the wavelength and the intensity of light incident on the light receiving portion. However, controlling the thickness of ARC layer 20 is difficult.
Additionally, prior to the formation of ARC layer 20, interlayer dielectric film 12 and inter-metal dielectric film 14 are selectively etched and removed in order to expose the surface of semiconductor substrate 1. However, the surface of semiconductor substrate 1 may be over-etched during this process. Over-etching causes damage to the surface of semiconductor substrate 1, and the damage increases leakage current. Still, the over-etching is required because the thickness of interlayer dielectric film 12 and inter-metal dielectric film 14 are different.
A shallow junction for a terminal is an important factor in improving the light efficiency. However, it is difficult to form the shallow junction because N+-type highly doped layer 8, P-type first junction region 4, P-type second junction region 6, P+-type layer 9b, and P+-type partition layer 9a are formed using implantation and heat-treatment processes which limit the improvement of the light efficiency.